CMP3006 Embedded Systems Programming Lecture 4: Digital Input, Lecture notes of Embedded Systems Programming

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CMP

EMBEDDED

SYSTEMS

PROGRAMMING

LECTURE 4 DIGITAL INPUT

Switches as Digital Input

Mechanical

Connecting Switches to a Digital

System

Single-pole double-throw (SPDT) connection

1 (HIGH)

0 (LOW)

𝜇𝐶

Connecting Switches to a Digital

System

Single-pole single-throw (SPST) connection

Pullup &Pulldown

𝜇𝐶

𝜇𝐶

I/O Ports

• Internal Pullups
  • (^) If a pin is an input (DDRxi = 0):
    • (^) PORTxi = 0 – pin is floating
    • PORTxi = 1 – connects a pullup to the pin
      • Keeps pin from floating if no one driving
      • Allows wired-OR bus

DDRxi PORTxi Function

Input - Floating

0 1 Input – internal Pullup connected

1 0 Output LOW

1 1 Output HIGH

Counting Event with Buttons

(Switch)

Mechanical

loop() {

b = digitalRead(0);

if(b == 1){

// PRESSED

digitalWrite(13,HIGH);

}

else{

digitalWrite(13,LOW);

}

}

count = 0;

loop() {

b = digitalRead(0);

if(b == 1){

count++;

}

}

count = 0;

presses = false;

loop() {

b = digitalRead(0);

if(b == 1 && !pressed){

count++;

pressed = true;

}

else

pressed = false;

}

Bouncing

Debouncing

INTEGRATED CIRCUIT

SOLUTIONS

Use switch debouncers like the MAX

Bouncing

Shift Register

int state =0;

loop() {

b = !digitalRead(0);

state= (state<<1) | b | 0xe000;

if(State==0xf000){

// PRESSED

}

}

0111111111111